[115.04] The Mass Function of Young Star Clusters in Merging Galaxies

B. W. Miller (Leiden Obs.), S. M. Fall (STScI)

We compare the observed color and luminosity distributions of
star cluster systems in the young merger remnants NGC 3921 and
NGC 7252 with evolutionary models in order to investigate the shape
of the mass function of young star clusters and the duration of
cluster formation. The color distribution constrains the mean
age of the young clusters and the period over which they formed.
The mean ages are 350--550 Myr for NGC 3921 and 650--850 Myr for
NGC 7252, while the burst durations are \lesssim400 Myr. None of
our models with a lognormal mass function for the young clusters
give good matches to the observations. However, models with a
power-law mass function are good representations of the data.

This result has important implications for the question of
whether young star clusters form by the same physical process as
old globular clusters, which have lognormal mass functions. The
differences may be due to how environmental conditions, including
metallicity, affect the Jeans mass of cooling gas. Or, it may be
that all clusters form from ``scale-free'' initial conditions and
dynamical processes preferentially distrupt low mass clusters.
More theoretical and observational work is being done to address
these issues.

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